Fig. 3.—German Balloon equipped for Meteorological Observations.
The reorganization of balloon observations was accomplished by the German Society for the Promotion of Aërial Navigation, which has been assisted by the Prussian Meteorological Institute, and by officers of the German Army Balloon Corps. The German Emperor takes a personal interest in the work, and has aided it by the gift of a considerable sum of money. The first voyage under the direction of the Society was made in 1888, and many notable ones followed. In 1891, through the courtesy of the president, Dr. Assmann, the writer made an ascent from Berlin in a balloon equipped for accurate observations, with the special purpose of comparing the sling with the aspiration thermometer. The car of the balloon is shown in [Fig. 3]. A companion was the now famous Dr. Berson, who then made his second ascent, but who has now become an expert aeronaut by reason of more than fifty ascensions, some of them to great heights. On December 4, 1894, he ascended alone from Stassfurt, Prussia, in the Phœnix, to probably the greatest height ever reached by man, at least in a conscious state. By breathing oxygen he was able to keep his senses and to read the barometer at 9·1 inches, indicating approximately an altitude of 30,000 feet, and the aspirated thermometer at 54° below zero. An ordinary thermometer read 11° below zero in the sun, showing its heat was much diminished in consequence of the haze that prevailed even at this enormous height. The cirriform clouds which surrounded the balloon were found to have the structure of snow-flakes rather than that of ice-crystals. The chief result of this record-breaking ascent was the extraordinarily low temperatures recorded at great heights, as compared with those observed by Glaisher, Tissandier, and others. An inversion of temperature—that is an increase of temperature with height—prevailed up to a mile, but above that the temperature fell at a rapid and accelerated rate which approached the adiabatic fall above 26,000 feet. The wind, which was almost calm at the earth's surface, increased to a gale in the high atmosphere, and carried the balloon along at an average speed of thirty-six miles an hour. Wishing to demonstrate conclusively whether the insular position of England influenced the temperature of the high atmosphere, as had been suggested, Dr. Berson determined to execute a high ascension in England during the prevalence of a barometric maximum in summer, when the air column would be abnormally warmed and the upper isothermal surfaces elevated. An opportunity was afforded Berson to follow in Glaisher's footsteps on September 14, 1898, when abnormal heat prevailed in Europe. Berson, with the aeronaut Spencer, in the balloon Excelsior, rose from the Crystal Palace in London to the height of 27,300 feet, where he observed a temperature of -29°. The oxygen inhaled prevented harmful physiological effects except for the discomfort caused by the enormous reduction of temperature from 80° at the ground only thirty-five minutes before. The temperature decreased rapidly at first, then moderately up to three miles, and above that it fell almost at the adiabatic rate. Even in this hot summer maximum of pressure and notwithstanding the maritime climate and south-westerly currents, a temperature about 29° below zero reigned at 27,000 feet, being only a few degrees warmer than Berson had observed in winter at the same height above Germany. Yet Glaisher, in all his ascents, two of which exceeded 26,000 feet, never recorded a temperature of less than 5° below zero. These relatively high temperatures, obtained also by Welsh, Tissandier, and Gay-Lussac, must be attributed to the insufficient protection of the thermometers against insolation, to the proximity of the instruments to the heated basket and its occupants, and lastly, to the sluggishness of the thermometers themselves, from lack of ventilation, during the rapid passage through air-strata of different temperatures. [Plate VI]. indicates the change of temperature with height observed during the four highest balloon ascents in Europe and in the United States. Dots indicate the observations while ascending, and crosses the observations while descending; these are connected by full and broken lines respectively, an inclination upward to the left showing a decrease of temperature with height and vice versâ. The adiabatic lines, representing a fall of temperature of 1° Fahrenheit per 183 feet of ascent, serve for comparison.
Plate VI.—Temperatures observed in Four High Balloon Ascents.
This account of notable balloon ascents should not be closed without mentioning the most daring and unique of all, the voyage of Mr. S. A. Andrée towards the north pole in 1897. Although his was a voyage of geographical discovery, and not one for the exploration of the air, yet meteorological and other observations were to be made, and Andrée had familiarized himself with the instruments and the management of a balloon during several voyages in Sweden. The success of the polar voyage depended primarily upon the prevalence of southerly winds, and the ability of the balloon to keep afloat long enough to profit by them, even should they be light and variable at times. Therefore the impermeability of the balloon to hydrogen gas was of vital importance, and it was the conviction that the Eagle, of 140,000 cubic feet, was neither sufficiently large nor staunch to sustain itself for thirty days, the time which might be required to reach Behring Straits, that led Dr. Nils Ekholm, the meteorologist and physicist, to withdraw from the expedition. Unfortunately, his fears seem to have been well founded, and it is probable that we must now abandon hope of the safety of the brave Andrée and his two companions.
A less perilous voyage northward across the Alps was attempted in 1898 by Professor Heim, the Swiss geologist, and two associates, conducted by the Italian aeronaut, Spelterini. With an automatic photographic camera, similar to one described in the next chapter, it was hoped to get views of the high Alps from above, which would be alike valuable for geologic and topographic study. Extensive meteorological observations were made in connection with the sixth international balloon ascent, but only the Jura was crossed, at an altitude of 13,000 feet, because the balloon travelled in a north-westerly direction, instead of north-east as was expected.
Many years ago Wise and Donaldson, the American aeronauts, proposed to cross the Atlantic Ocean in a balloon. The difficulties which present themselves in such an undertaking are purely technical, and given a balloon which loses its gas so slowly that its buoyancy can be maintained for several days, there seems to be no reason why such a balloon, at a height of four or five miles, could not pass from San Francisco to New York, or from the United States to Europe, since the motion of the upper clouds proves that the high atmosphere moves almost constantly with great velocity from the west to the east. The dirigible balloon has not been realized except in nearly calm weather, but the aeronaut can often reverse his direction by ascending or descending into a contrary wind to that in which he has been travelling. Frequently no clouds separate these opposing currents, which become apparent only when a balloon enters them.
It has been mentioned that in 1869 Glaisher made observations in a captive balloon in England up to the height of 1700 feet in order to study the conditions of the air within this distance of the earth, which could not be done in a free and rapidly moving balloon. Although captive balloons are frequently used in the European cities to lift people who wish to enjoy the view from a height of 500 or 1000 feet, they appear to have been little used by scientific observers since the time of Glaisher. In 1890-91 the aeronautical society at Berlin employed a captive balloon in connection with the observations in free balloons which have been described. This captive balloon had a capacity of only 5000 cubic feet, but it sufficed to lift an apparatus weighing sixteen pounds, designed by Dr. Assmann to record atmospheric pressure, as well as the temperature and relative humidity of the air. The balloon, attached to a cable 2600 feet long, was drawn down by a steam engine. It was possible in this way to have simultaneous observations at three levels, viz. near the ground, in the free air at a height of about half-a-mile, and at the highest level attained by a free balloon. But the captive balloon is often at a disadvantage, for the wind drives it down, and although the meteorograph mentioned had ingenious devices to neutralize the violent shocks caused by this and by the rebound of the balloon after the gust of wind, yet these impaired the automatic record. The height to which the balloon rose was so much diminished by the wind that instead of 2600 feet, which the balloon attained in calm weather when the cable was vertical, the average height of the twenty-four ascents was but half this, and in very windy weather the balloon could not rise at all.